[Qemu-devel] [PATCH 2/3] Introduce a 'client_add' monitor command accepting an open FD

[Daniel P. Berrange]

Allow client connections for VNC and socket based character
devices to be passed in over the monitor using SCM_RIGHTS.

One intended usage scenario is to start QEMU with VNC on a
UNIX domain socket. An unprivileged user which cannot access
the UNIX domain socket, can then connect to QEMU's VNC server
by passing an open FD to libvirt, which passes it onto QEMU.

 { "execute": "get_fd", "arguments": { "fdname": "myclient" } }
 { "return": {} }
 { "execute": "add_client", "arguments": { "protocol": "vnc",
                                           "fdname": "myclient",
                                           "skipauth": true } }
 { "return": {} }

In this case 'protocol' can be 'vnc' or 'spice', or the name
of a character device (eg from -chardev id=XXXX)

The 'skipauth' parameter can be used to skip any configured
VNC authentication scheme, which is useful if the mgmt layer
talking to the monitor has already authenticated the client
in another way.

* console.h: Define 'vnc_display_add_client' method
* monitor.c: Implement 'client_add' command
* qemu-char.c, qemu-char.h: Add 'qemu_char_add_client' method
* qerror.c, qerror.h: Add QERR_ADD_CLIENT_FAILED
* qmp-commands.hx: Declare 'client_add' command
* ui/vnc.c: Implement 'vnc_display_add_client' method
---
 console.h       |    1 +
 monitor.c       |   32 ++++++++++++++++++++++++++++++++
 qemu-char.c     |   30 ++++++++++++++++++++++++------
 qemu-char.h     |    2 ++
 qerror.c        |    4 ++++
 qerror.h        |    3 +++
 qmp-commands.hx |   27 +++++++++++++++++++++++++++
 ui/vnc.c        |    7 +++++++
 8 files changed, 100 insertions(+), 6 deletions(-)

diff --git a/console.h b/console.h
index 64d1f09..84d3e8d 100644
--- a/console.h
+++ b/console.h
@@ -372,6 +372,7 @@ void cocoa_display_init(DisplayState *ds, int full_screen);
 void vnc_display_init(DisplayState *ds);
 void vnc_display_close(DisplayState *ds);
 int vnc_display_open(DisplayState *ds, const char *display);
+void vnc_display_add_client(DisplayState *ds, int csock, int skipauth);
 int vnc_display_disable_login(DisplayState *ds);
 char *vnc_display_local_addr(DisplayState *ds);
 #ifdef CONFIG_VNC
diff --git a/monitor.c b/monitor.c
index 6af6a4d..23c310e 100644
--- a/monitor.c
+++ b/monitor.c
@@ -1185,6 +1185,38 @@ static int expire_password(Monitor *mon, const QDict 
*qdict, QObject **ret_data)
     return -1;
 }
 
+static int add_graphics_client(Monitor *mon, const QDict *qdict, QObject 
**ret_data)
+{
+    const char *protocol  = qdict_get_str(qdict, "protocol");
+    const char *fdname = qdict_get_str(qdict, "fdname");
+    int skipauth = qdict_get_try_bool(qdict, "skipauth", 0);
+    CharDriverState *s;
+
+    if (strcmp(protocol, "spice") == 0) {
+        if (!using_spice) {
+            /* correct one? spice isn't a device ,,, */
+            qerror_report(QERR_DEVICE_NOT_ACTIVE, "spice");
+            return -1;
+        }
+       qerror_report(QERR_ADD_CLIENT_FAILED);
+       return -1;
+    } else if (strcmp(protocol, "vnc") == 0) {
+       int fd = monitor_get_fd(mon, fdname);
+       vnc_display_add_client(NULL, fd, skipauth);
+       return 0;
+    } else if ((s = qemu_chr_find(protocol)) != NULL) {
+       int fd = monitor_get_fd(mon, fdname);
+       if (qemu_chr_add_client(s, fd) < 0) {
+           qerror_report(QERR_ADD_CLIENT_FAILED);
+           return -1;
+       }
+       return 0;
+    }
+
+    qerror_report(QERR_INVALID_PARAMETER, "protocol");
+    return -1;
+}
+
 static int client_migrate_info(Monitor *mon, const QDict *qdict, QObject 
**ret_data)
 {
     const char *protocol = qdict_get_str(qdict, "protocol");
diff --git a/qemu-char.c b/qemu-char.c
index fb13b28..4e168ee 100644
--- a/qemu-char.c
+++ b/qemu-char.c
@@ -168,6 +168,11 @@ int qemu_chr_get_msgfd(CharDriverState *s)
     return s->get_msgfd ? s->get_msgfd(s) : -1;
 }
 
+int qemu_chr_add_client(CharDriverState *s, int fd)
+{
+    return s->chr_add_client ? s->chr_add_client(s, fd) : -1;
+}
+
 void qemu_chr_accept_input(CharDriverState *s)
 {
     if (s->chr_accept_input)
@@ -2123,6 +2128,22 @@ static void socket_set_nodelay(int fd)
     setsockopt(fd, IPPROTO_TCP, TCP_NODELAY, (char *)&val, sizeof(val));
 }
 
+static int tcp_chr_add_client(CharDriverState *chr, int fd)
+{
+    TCPCharDriver *s = chr->opaque;
+    if (s->fd != -1)
+       return -1;
+
+    socket_set_nonblock(fd);
+    if (s->do_nodelay)
+        socket_set_nodelay(fd);
+    s->fd = fd;
+    qemu_set_fd_handler(s->listen_fd, NULL, NULL, NULL);
+    tcp_chr_connect(chr);
+
+    return 0;
+}
+
 static void tcp_chr_accept(void *opaque)
 {
     CharDriverState *chr = opaque;
@@ -2155,12 +2176,8 @@ static void tcp_chr_accept(void *opaque)
             break;
         }
     }
-    socket_set_nonblock(fd);
-    if (s->do_nodelay)
-        socket_set_nodelay(fd);
-    s->fd = fd;
-    qemu_set_fd_handler(s->listen_fd, NULL, NULL, NULL);
-    tcp_chr_connect(chr);
+    if (tcp_chr_add_client(chr, fd) < 0)
+       close(fd);
 }
 
 static void tcp_chr_close(CharDriverState *chr)
@@ -2230,6 +2247,7 @@ static CharDriverState *qemu_chr_open_socket(QemuOpts 
*opts)
     chr->chr_write = tcp_chr_write;
     chr->chr_close = tcp_chr_close;
     chr->get_msgfd = tcp_get_msgfd;
+    chr->chr_add_client = tcp_chr_add_client;
 
     if (is_listen) {
         s->listen_fd = fd;
diff --git a/qemu-char.h b/qemu-char.h
index 892c6da..f361c6d 100644
--- a/qemu-char.h
+++ b/qemu-char.h
@@ -57,6 +57,7 @@ struct CharDriverState {
     void (*chr_update_read_handler)(struct CharDriverState *s);
     int (*chr_ioctl)(struct CharDriverState *s, int cmd, void *arg);
     int (*get_msgfd)(struct CharDriverState *s);
+    int (*chr_add_client)(struct CharDriverState *chr, int fd);
     IOEventHandler *chr_event;
     IOCanReadHandler *chr_can_read;
     IOReadHandler *chr_read;
@@ -99,6 +100,7 @@ int qemu_chr_can_read(CharDriverState *s);
 void qemu_chr_read(CharDriverState *s, uint8_t *buf, int len);
 int qemu_chr_get_msgfd(CharDriverState *s);
 void qemu_chr_accept_input(CharDriverState *s);
+int qemu_chr_add_client(CharDriverState *s, int fd);
 void qemu_chr_info_print(Monitor *mon, const QObject *ret_data);
 void qemu_chr_info(Monitor *mon, QObject **ret_data);
 CharDriverState *qemu_chr_find(const char *name);
diff --git a/qerror.c b/qerror.c
index d7fcd93..79be1ba 100644
--- a/qerror.c
+++ b/qerror.c
@@ -193,6 +193,10 @@ static const QErrorStringTable qerror_table[] = {
         .desc      = "Could not set password",
     },
     {
+        .error_fmt = QERR_ADD_CLIENT_FAILED,
+        .desc      = "Could not add client",
+    },
+    {
         .error_fmt = QERR_TOO_MANY_FILES,
         .desc      = "Too many open files",
     },
diff --git a/qerror.h b/qerror.h
index 16c830d..25773cd 100644
--- a/qerror.h
+++ b/qerror.h
@@ -163,6 +163,9 @@ QError *qobject_to_qerror(const QObject *obj);
 #define QERR_SET_PASSWD_FAILED \
     "{ 'class': 'SetPasswdFailed', 'data': {} }"
 
+#define QERR_ADD_CLIENT_FAILED \
+    "{ 'class': 'AddClientFailed', 'data': {} }"
+
 #define QERR_TOO_MANY_FILES \
     "{ 'class': 'TooManyFiles', 'data': {} }"
 
diff --git a/qmp-commands.hx b/qmp-commands.hx
index 92c5c3a..1e19abc 100644
--- a/qmp-commands.hx
+++ b/qmp-commands.hx
@@ -885,6 +885,33 @@ Example:
 EQMP
 
     {
+        .name       = "add_client",
+        .args_type  = "protocol:s,fdname:s,skipauth:b?",
+        .params     = "protocol fdname skipauth",
+        .help       = "add a graphics client",
+        .user_print = monitor_user_noop,
+        .mhandler.cmd_new = add_graphics_client,
+    },
+
+SQMP
+add_client
+----------
+
+Add a graphics client
+
+Arguments:
+
+- "protocol": protocol name (json-string)
+- "fdname": file descriptor name (json-string)
+
+Example:
+
+-> { "execute": "add_client", "arguments": { "protocol": "vnc",
+                                             "fdname": "myclient" } }
+<- { "return": {} }
+
+EQMP
+    {
         .name       = "qmp_capabilities",
         .args_type  = "",
         .params     = "",
diff --git a/ui/vnc.c b/ui/vnc.c
index 39b5b51..8602adc 100644
--- a/ui/vnc.c
+++ b/ui/vnc.c
@@ -2924,3 +2924,10 @@ int vnc_display_open(DisplayState *ds, const char 
*display)
     }
     return qemu_set_fd_handler2(vs->lsock, NULL, vnc_listen_read, NULL, vs);
 }
+
+void vnc_display_add_client(DisplayState *ds, int csock, int skipauth)
+{
+    VncDisplay *vs = ds ? (VncDisplay *)ds->opaque : vnc_display;
+
+    return vnc_connect(vs, csock, skipauth);
+}
-- 
1.7.4.4